New York-based Pershing Square bought up a 9.8% stake in Air Products & Chemicals, a Pennsylvania-based industrial-gas producer. The hedge fund about $2.05 billion for the shares, which are up 30% this year.

Air Products is the target of the $1 billion single-stock fund Pershing Square announced earlier this month. Countering reports that the hedge fund was having difficulty raising money for that vehicle, Ackman told Bloomberg News that Pershing Square raised "more than we could spend." Pershing Square's existing hedge funds also invested in the stake.

Ackman's move sets up a potential battle with Air Products, which last week adopted a poison pill provision to prevent any investor from gaining too much control. The company said it "looks forward to engaging with Pershing Square to understand its views."

Ackman has yet to make his demands for Air Products clear. But in fundraising documents for the single-stock special-purpose vehicle, he noted that the company he had in mind trades at a lower multiple than its closest competitor.

"The company has lower margins than a lot of its peers," SunTrust Robinson Humphrey analyst James Sheehan told Bloomberg Radio. "He may push for them to divest some of their non-core businesses." Sources told The Wall Street Journal that Ackman does not plan to push for a break-up of the company.